1. Technical Field
The present invention pertains to improvements in methods and apparatus for heating or cooling sterile surgical liquids and collecting surgical sterile slush. In particular, the invention is an improvement of the methods and apparatus disclosed in U.S. Pat. Nos. 4,393,659 (Keyes et al), 4,934,152 (Templeton), 5,163,299 (Faries, Jr. et al), 5,331,280 (Faries, Jr. et al), 5,333,326 (Faries, Jr. et al), and copending U.S. patent application Ser. No. 08/336,423, filed Oct. 20, 1994. The disclosures in those patents and applications are expressly incorporated by reference herein in their entireties.
2. Discussion of the Prior Art
The above-referenced Keyes et al patent discloses a surgical slush producing system having a cabinet with a heat transfer basin at its top surface. A refrigeration mechanism in the cabinet takes the form of a closed refrigeration loop including: an evaporator in heat exchange relation to the outside surface of the heat transfer basin; a compressor; a condenser; and a refrigeration expansion control, all located within the cabinet. A separate product basin is configured to be removably received in the heat transfer basin. Spacers, in the form of short cylindrical stubs or buttons, are arranged in three groups spaced about the heat transfer basin and projecting into the heat transfer basin interior to maintain a prescribed space between the two basins. During use, that space contains a thermal transfer liquid, such as alcohol or glycol, serving as a thermal transfer medium between the two basins. A sterile drape, impervious to the thermal transfer medium, is disposed between the product basin exterior and the liquid thermal transfer medium to preserve the sterile nature of the product basin. Surgically sterile liquid, such as sodium chloride solution, is placed in the product basin and congeals on the side of that basin when the refrigeration unit is activated. A scraping tool is utilized to remove congealed sterile material from the product basin side to thereby form a slush of desired consistency within the product basin. Some users of the system employ the scraping tool to chip the solid pieces from the basin side.
As noted in the above-referenced Templeton patent, the Keyes et al system has a number of disadvantages. In particular, the separate product basin must be removed and re-sterilized after each use. Additionally, the glycol or other thermal transfer medium is highly flammable or toxic and, in any event, complicates the procedure. The Templeton patent discloses a solution to these problems by constructing an entirely new apparatus whereby the product basin is eliminated in favor of a sterile drape impervious to the sterile surgical liquid, the drape being made to conform to the basin and directly receive the sterile liquid. Congealed liquid is scraped or chipped from the sides of the conformed drape receptacle to form the desired surgical slush.
The Faries, Jr. et al U.S. Pat. No. (5,163,299) notes that scraping congealed liquid from the drape is undesirable in view of the potential for damage to the drape, resulting in a compromise of sterile conditions. As a solution to the problem, the patent proposes that the drape be lifted or otherwise manipulated by hand to break up the congealed liquid adhering to the drape. Although this hand manipulation is somewhat effective, it is not optimal, and often is inconvenient and constitutes an additional chore for operating room personnel.
The Faries, Jr. et al U.S. Pat. No. (5,331,820) resolves the problem of manual manipulation of the drape by providing a method and apparatus to automatically remove the congealed liquid adhering to the drape without endangering the integrity of the drape. A flat disk or plate is provided at the bottom of the basin under the drape. The plate is moved in an up and down matter to disengage the congealed liquid from the drape. The plate may be attached to a mechanism below the basin, or to the drape itself as disclosed in copending U.S. patent application Ser. No. 08/336,423.
Templeton further provides an electrical heater disposed at the bottom of the basin to convert the sterile slush to warmed liquid, or to heat additional sterile liquid added to the basin. Templeton describes the need for such warm sterile liquid as occurring after a surgical procedure is completed to facilitate raising the body cavity of the surgery patient back to its normal temperature by contact with the warmed liquid. However, there are a number of instances during a surgical procedure when it is desirable to have simultaneous access to both the sterile warmed liquid and the sterile surgical slush. The Faries, Jr. et al (5,333,326) patent provides a method and apparatus for simultaneously providing separate surgical slush and warmed surgical liquid during a surgical procedure using a single drape for such a unit.
The foregoing patents do not provide a way to prevent damage to the heating and cooling mechanisms when there is no liquid present in the respective basins. Further, the foregoing patents do not provide a way to detect leaks in a surgical drape. Specifically, when insignificant amounts of liquid are present in the basins, the heating and cooling mechanisms operate with little thermal resistance, thereby making burn out of the mechanisms likely. Another consequence is that the drapes are damaged by being attached to the heating or cooling mechanism without having the liquid to absorb the thermal energy. Since only sterile drapes are to be used during surgical procedures, a leak in a surgical drape compromises sterility and contaminates the entire surgical procedure, thereby increasing the risk of injury to the patient.